Hydrogel Based Formulations of Imazethapyr: Development and Appraisal of Release Behaviour

VIKAS KUMAR

Hydrogel Based Formulations of Imazethapyr: Development and Appraisal of Release Behaviour

Date

2014

Authors

VIKAS KUMAR

Publisher

Division of Agricultural Chemicals Indian Agricultural Research Institute New Delhi

Abstract

Imazethapyr, a systemic broad spectrum herbicide is recommended for soybean, groundnuts and other leguminous crops. Primarily applied as postemergence, its use is also recommended for pre emergence weed control. In India, its liquid formulation in the form of soluble liquid (SL) is largely used whose preparation involves the use of surfactants, emulsifiers and inorganic salts. This, coupled with fast dissipation in water necessitates the development of controlled release formulations of imazethapyr that are simple to prepare, possess slow release properties and involve minimal or no use of toxic adjuvants. The objective of present thesis was to develop hydrogel based controlled release formulations of imazethapyr for pre and post emergence application, to evaluate their release behaviour in water and bioefficacy against prevalent weeds in a kharif/rabi crop. Guar gum (GG), a galactomannan polysaccharide was employed to prepare novel GG-g-polyacrylate/bentonite superporous hydrogel composites (GG-SPHC) and core shell nanogels (GG-CSH) as carriers. Reaction factors, the backbone-monomer ratio, cross linker, bentonite and porogen contents were optimized w.r.t swelling characteristics. The prepared hydrogels were characterized by FT-IR, X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Swelling behaviour of the representative GG-SPHC was evaluated w.r.t. salt and fertilizer solutions, temperature, water quality and pH. GGSPHC exhibited very fast swelling (30 minutes), almost similar to the corresponding clay free hydrogel. Higher absorbency under load as compared to the clay free gel showed improved mechanical strength of the composites. The core-shell nanogels (GG-shell-PNIPAm-core; GG-shell-PVA-core; PNIPAm-shell-GG-PVA-core) exhibited mean particle size in the range of 11 nm to 490 nm. TEM analysis exhibited core shell spherical structures of prepared nanogels. GG-SPHC and GG-CSH carriers with optimized compositions were used to prepare imazethapyr formulations of imazethapyr under ambient conditions. The release of a.i. from the all the test compositions in water followed Fickian mechanism. Release was faster in GG-SPHC formulations (t1/2 =4.4 to 12.6 days). Field appraisal on bioefficacy of prepared formulations vis-a-vis commercial formulations showed very high weed control index of test formulation (96.7- 99.1% on 90 DAS) comparable to that of commercial formulations (98-99.4%). GG-SPHC formulations of imazethapyr applied at pre-emergence stage, exhibited significantly higher weed control as compared to other formulation treatments. All the imazethapyr formulations exhibited acute phytotoxicity in garlic crop (variety G 41) implying that its use in garlic crop and varietal response to imazethapyr and its formulations need further investigations.